Ameliorative effects of Lanthanum(III) on Copper(II) stressed rice (Oryza sativa) and its molecular mechanism revealed by transcriptome profiling

Rare earth elements are known to alleviate heavy metal stress. However, the potential mechanisms of the alleviation remain unclear. This study compared the effects of La(NO3)(3) and La(NO3)(3)-amino acid chelates (La (III)-AA) on growth, oxidative stress, ultrastructure, bioaccumulation and gene expression in rice. Results demonstrated that 20 mg/L La (III)-AA can effectively ameliorate CuSO4 (50 mg/L) stress in rice by reducing oxidative stress and increasing chlorophyll content, thus promoting growth. ICP and TEM revealed an antagonistic effect between La (III) and Cu(II). Exogenous La (III)-AA decreased Cu(II) content in rice leaves, stems and roots by 55.56%, 59.46% and 26.29%, and ameliorated Cu(II) damage by maintaining the ultrastructure of mesophyll cells. RNA sequencing identified 7020 differentially expressed genes, and 8 were validated by qRT-PCR. Indole-3-acetic acid (IAA) concentration was detected by HPLC. Correlation analysis between OsGH3.4-IAA-Expansin revealed that IAA content is negatively correlated with OsGH3.4 (r = -0.82, P < 0.05), and positively correlated with Expansin (r = 0.78, P < 0.05). It's assumed that La (III)-induced OsGH3.4 could inhibit IAA-dependent Expansin expression, thereby conferring resistance to Cu stress. This work provides novel insights into the molecular basis underlying La (III)-induced Cu(II) tolerance in rice.